1. Field of Invention
The invention is an etching method for making fluid bearings and, in particular, to a method for making the oil groove in the inner diameter of the fluid bearing.
2. Related Art
In mechanical designs, making passive fluid bearings requires an oil groove in the inner diameter of the bearing, so that a good oil film pressure and oil seal can be generated during the operation of the bearing. The oil groove in a normal bearing is made by cutting in the conventional machining. However, the motors become smaller and it is not easy to make micro motors that require high precisions. Such micro motors have strict requirements on the depth and width of the oil groove and the concentricity of the inner diameter of the bearing. If they are still made using the conventional cutting technique, there can easily be such problems of rough edges, bad oil groove concentricity, blade erosion, and difficulty in making machining blades.
The Japanese-based Hitachi, Inc proposed to use a metal to roll on the inner surface of the bearing, pressing on the surface to produce the desired oil groove. This technique is disclosed in the U.S. Pat. No. 5,758,421, and is the main technology of making fluid bearing products. However, this kind of method of using a rolling metal ball has a small contact area between the metal and the bearing, resulting in erosion. Besides, since the metal ball for making the oil groove is extremely small, consequently the metal ball holding tool is hard to design and produce. Moreover, a precisely positioned control platform is also required for the rolling.
In addition, there is a technology of using plastic injection molding to make the fluid bearing, as disclosed in the U.S. Pat. No. 6,074,098. This method utilizes the elasticity of the plastic to force the plastic bearing formed by ejection molding to leave the mold. The problem, however, is that the rigidity and hardness of the plastic bearing are not strong enough against erosion.